Game Theory : Two-person, Constant-Sum Games

The attached file has a problem that I can't figure out how to set up. Can you take a look and explain how this problem should be set up?

There are two people playing a two-person constant-sum game. Player 1 wants to travel from New York to Dallas using the shortest of the possible routes listed below. Player 2 has the ability to block one route out of Atlanta and one route out of Nashville. Player 1 will not know which roads are blocked until the arrival at Atlanta or Nashville. Should Player 1 start towards Atlanta or Nashville? Which routes should Player 2 block?